Magnetoresistance effect element

ABSTRACT

A magnetoresistance effect element has a first ferromagnetic metal layer, a second ferromagnetic metal layer, and a tunnel barrier layer that is sandwiched between the first and second ferromagnetic metal layers, and the tunnel barrier layer has a spinel structure in which cations are disordered, and contains a divalent cation of a non-magnetic element, a trivalent cation of a non-magnetic element, oxygen, and one of nitrogen and fluorine.

This is a continuation-in-part of application Ser. No. 16/587,178, filed Sep. 30, 2019, which is a continuation of application Ser. No. 16/142,112 filed Sep. 26, 2018, which is a continuation of application Ser. No. 15/559,195 filed Sep. 18, 2017, which is a National Stage Application of PCT/JP2016/059949 filed Mar. 28, 2016, and claims the benefit of Japanese Application No. 2015-071414 filed Mar. 31, 2015. The entire disclosures of the prior applications are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a magnetoresistance effect element.

Priority is claimed on Japanese Patent Application No. 2015-071414, filed on Mar. 31, 2015, the content of which is incorporated herein by reference.

BACKGROUND ART

A giant magnetoresistance (GMR) elements formed of a multilayer film consisting of a ferromagnetic layer and a non-magnetic layer, and tunnel magnetoresistance (TMR) elements using an insulating layer (a tunnel barrier layer or a barrier layer) as a non-magnetic layer have been known. In general, TMR elements have higher element resistance than GMR elements, but a magnetoresistance (MR) ratio of the TMR elements is higher than that of the GMR elements. The TMR elements can be divided into two types. One type is related to TMR elements using only a tunneling effect using an effect of soaking-out of a wave function between ferromagnetic layers. The other type is related to TMR elements using coherent tunneling using conduction in a specific orbit of a non-magnetic insulating layer where tunneling is carried out when the above-described tunneling effect is caused. TMR elements using coherent tunneling have been known to obtain a higher MR ratio than TMR elements using only tunneling. The coherent tunneling effect is caused in a case where both of the ferromagnetic layer and the non-magnetic insulating layer are crystalline and an interface between the ferromagnetic layer and the non-magnetic insulating layer is crystallographically continuous.

Magnetoresistance effect elements are used for various purposes. For example, magnetoresistance effect-type magnetic sensors have been known as magnetic sensors, and magnetoresistance effect elements determine characteristics of a reproducing function of hard disk drives. Magnetic sensors have a system that detects, as a resistance change of a magnetoresistance effect element, an effect that a magnetization direction of the magnetoresistance effect element is changed by an external magnetic field. Highly anticipated devices are magnetoresistance change-type random access memories (MRAM). MRAMs are memories that read magnetoresistance as digital signals of 0 and 1 by appropriately changing ferromagnetic magnetization directions of two layers to parallel or antiparallel directions.

LITERATURE

-   [Patent Document 1] Japanese Patent No. 5586028 -   [Patent Document 2] Japanese Unexamined Patent Application, First     Publication No. 2013-175615 -   [Non-Patent Document 1] Hiroaki Sukegawa, a [1] Huixin Xiu,     Tadakatsu Ohkubo, Takao Furubayashi, Tomohiko Niizeki, Wenhong Wang,     Shinya Kasai, Seiji Mitani, Koichiro Inomata, and Kazuhiro Hono,     APPLIED PHYSICS LETTERS 96, 212505 [1] (2010) -   [Non-Patent Document 2] Thomas Scheike, Hiroaki Sukegawa, Takao     Furubayashi, Zhenchao Wen, Koichiro Inomata, Tadakatsu Ohkubo,     Kazuhiro Hono, and Seiji Mitani, Applied Physics Review, 105, 242407     (2014) -   [Non-Patent Document 3] Yoshio Miura, Shingo Muramoto, Kazutaka Abe,     and Masafumi Shirai, Physical Review B 86, 024426 (2012)

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

A tunnel barrier having a spinel structure has been reported to be effective as a substituent material for MgO. A spinel tunnel barrier expressed by a composition formula of MgAl₂O₄ has been known to obtain the same MR ratio as MgO, and to obtain a higher MR ratio than MgO at a high bias voltage. However, the spinel tunnel barrier has a difficulty in making area resistance (RA) lower than that of MgO while maintaining the MR ratio.

Future devices such as magnetic sensors and MRAMs are required to obtain a sufficiently high MR ratio even at a high bias voltage. In a magnetic sensor, an electrical signal obtained as a resistance change in a circuit should be amplified in order to observe a minute magnetic field such as geomagnetism or biomagnetism. In order to realize higher sensitivity than conventional sensors, as well as the MR ratio, an output voltage or an output current is also required to be increased, and driving at a high bias voltage is also required. In a case of MRAM, high-voltage driving is required in a write operation. In spin transfer torque-type (STT) MRAMs, the more the magnetization direction of a ferromagnetic layer changes, the higher current density is required to be applied to the magnetoresistance effect element. The magnetization direction of a ferromagnetic layer is an effect of the action of a spin-polarized current on the spin of the ferromagnetic layer. Similarly to the MR ratio, a rewrite current is generated by a strong spin-polarized current, and thus a high MR ratio is similarly required at a high bias voltage in STT-MRAMs.

In Patent Document 1 and Non-Patent Document 1, a tunnel barrier having a spinel structure is reported to be effective as a substituent material for MgO. A spinel tunnel barrier expressed by a composition formula of MgAl₂O₄ has been known to obtain the same MgO ratio as MgO, and to obtain a higher MR ratio than MgO at a high bias voltage. In addition, in Patent Document 2 and Non-Patent Documents 2 and 3, there is a description that MgAl₂O₄ is required to have a disordered spinel structure in order to obtain a high MR ratio. The above-described disordered spinel structure denotes a structure where oxygen atoms are arranged in cubic close-packed lattice that is substantially similar to spinel lattice, the structure as a whole belongs to a cubic structure, but arrangement of magnesium and aluminum atoms are disordered. In an original ordered spinel, Mg and Al are arranged in order in the tetrahedral vacancies and octahedral vacancies in the original spinel. However, since these are arranged in random arrangement in the disordered spinel structure, the crystal symmetry of the structure is different from MgAl₂O₄, and the lattice constant of the structure is substantially half of 0.808 nm of MgAl₂O₄.

The invention is contrived in view of the above-described circumstances, and an object thereof is to provide a magnetoresistance effect element that obtains a high MR ratio with lower RA than TMR elements using a conventional spinel tunnel barrier.

Means for Solving the Problem

In order to solve the above-described problems, a magnetoresistance effect element according to the invention has a first ferromagnetic metal layer, a second ferromagnetic metal layer, and a tunnel barrier layer that is sandwiched between the first and second ferromagnetic metal layers, and the tunnel barrier layer has a spinel structure in which cations are disordered, and contains a divalent cation of a non-magnetic element, a trivalent cation of a non-magnetic element, oxygen, and one of nitrogen and fluorine.

In a case where a different non-magnetic element is disposed in an oxygen site of the spinel structure of the tunnel barrier layer, the basic lattice constant is half the lattice constant of a conventional spinel structure, and the MR ratio is increased.

In the magnetoresistance effect element, the tunnel barrier layer may have a lattice-matched portion that is lattice-matched with both of the first ferromagnetic metal layer and the second ferromagnetic metal layer, and a lattice-mismatched portion that is not lattice-matched with at least one of the first ferromagnetic metal layer and the second ferromagnetic metal layer.

In the magnetoresistance effect element, a volume ratio of the lattice-matched portion in the tunnel barrier layer with respect to a volume of the entire tunnel barrier layer may be 65% to 95%.

In a case where the volume ratio of the lattice-matched portion in the tunnel barrier layer is 65% or less, the effect of coherent tunneling decreases, and thus the MR ratio is reduced. In a case where the volume ratio of the lattice-matched portion in the tunnel barrier layer is 95% or greater, the interference effect between the spin-polarized electrons during passing through the tunnel barrier layer does not decrease, and thus an increase in passage of the spin-polarized electrons through the tunnel barrier layer is not observed. By making the number of constituent elements of the non-magnetic element smaller than half the number of elements of the aluminum ion, vacancies are generated in the cation sites, the vacancies and two or more types of non-magnetic elements occupy the cations sites, and thus lattice periodicity is disturbed. Accordingly, the MR ratio is further increased.

In the magnetoresistance effect element, the tunnel barrier layer may have a cubic structure as a basic structure. In a case where the tunnel barrier layer has a cubic structure, contribution of tunnel orbits out of specific tunnel orbits is reduced, and the MR ratio is increased. The tunnel barrier layer exhibits its property even if its structure slightly deviates from the cubic structure. However, in a case where the tunnel barrier layer has a cubic structure, a higher MR ratio is shown.

In the magnetoresistance effect element, the divalent cation of a non-magnetic element may be any one selected from the group consisting of magnesium, zinc, and cadmium. These non-magnetic elements are stable in a case where the number of valence is 2, and in a case where these are constituent elements of the tunnel barrier layer, coherence tunneling can be realized, and the MR ratio is increased.

In the magnetoresistance effect element, the trivalent cation in a non-magnetic element may be any one selected from the group consisting of aluminum, gallium, and indium. These non-magnetic elements are stable in a case where the number of valence is 3, and in a case where these are constituent elements of the tunnel barrier layer, coherence tunneling can be realized, and the MR ratio is increased.

In the magnetoresistance effect element, in the tunnel barrier layer, the divalent cation of a non-magnetic element may be composed of a plurality of elements. In a case where a plurality of divalent cations are contained, disorder is promoted, and the MR ratio is increased.

In the magnetoresistance effect element, in the tunnel barrier layer, the trivalent cation of a non-magnetic element may be composed of a plurality of elements. In a case where a plurality of trivalent cations are contained, disorder is promoted, and the MR ratio is increased.

In the magnetoresistance effect element, the amount of the divalent cation of a non-magnetic element may be smaller than half the amount of the trivalent cation of a non-magnetic element in the tunnel barrier layer. By making the amount of the divalent cation of a non-magnetic element smaller than the amount of the trivalent cation of a non-magnetic element, the lattice constant of the tunnel barrier layer is reduced, and lattice matching with the ferromagnetic metal layer is improved. Thus, a high MR ratio can be maintained even at a high voltage.

In the magnetoresistance effect element, the amount of nitrogen or fluorine contained in the tunnel barrier layer may be 5.2% or less of an anion amount of the tunnel barrier layer. Although depending on the composition ratio, the maximum content of nitrogen or fluorine is up to 10% of a cation amount, and an increase in the MR ratio and a reduction in the RA are observed in a case where the cation amount is 5.2% or less. This indicates that bandgap narrowing effect is made by the level of nitrogen or fluorine partially substituted with oxygen functions.

In the magnetoresistance effect element, the lattice constant of the tunnel barrier layer is preferably 7.9186 Å to 8.9335 Å. In a case where the lattice constant of the tunnel barrier layer is 7.9186 Å to 8.9335 Å, it is observed that the tunnel barrier layer contains nitrogen or fluorine, and thus at least the MR ratio is the same or higher, and the resistance is reduced.

In the magnetoresistance effect element, the first ferromagnetic metal layer may have larger coercivity than the second ferromagnetic metal layer. Since the coercivity of the first ferromagnetic metal layer is different from that of the second ferromagnetic metal layer, the element functions as a spin valve, which allows for device applications.

In the magnetoresistance effect element, at least one of the first ferromagnetic metal layer and the second ferromagnetic metal layer may have magnetic anisotropy perpendicular to a stacking direction. Since it is not necessary to apply a bias magnetic field, it is possible to reduce the device in size. In addition, the element can be allowed to function as a recording element since it has high thermal disturbance resistance.

In the magnetoresistance effect element, at least one of the first ferromagnetic metal layer and the second ferromagnetic metal layer may be Co₂Mn_(1-a)Fe_(a)Al_(b)Si_(1-b) (0≤a≤1, 0≤b≤1). Co₂Mn_(1-a)Fe_(a)Al_(b)Si_(1-b) is a ferromagnetic metal material having high spin polarizability, and a higher MR ratio can be obtained than in a case where another ferromagnetic metal material is used.

Advantageous Effects

According to the invention, it is possible to provide a magnetoresistance effect element that obtains a high MR ratio with lower RA than TMR elements using a conventional spinel tunnel barrier.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a stacked structure of a magnetoresistance effect element.

FIG. 2 is a diagram of a crystal structure of a spinel.

FIG. 3 is a schematic diagram of an ordered spinel structure and a disordered spinel structure with symmetry of Fm-3m having a lattice constant assumed in a tunnel barrier layer of the invention.

FIG. 4 is a schematic diagram of an ordered spinel structure and a disordered spinel structure with symmetry of Fm-3m having a lattice constant assumed in a tunnel barrier layer of the invention.

FIG. 5 is a schematic diagram of an ordered spinel structure and a disordered spinel structure with symmetry of Fm-3m having a lattice constant assumed in a tunnel barrier layer of the invention.

FIG. 6 is a schematic diagram of an ordered spinel structure and a disordered spinel structure with symmetry of F-43m having a lattice constant assumed in a tunnel barrier layer of the invention.

FIG. 7 is a schematic diagram of an ordered spinel structure and a disordered spinel structure with symmetry of F-43m having a lattice constant assumed in a tunnel barrier layer of the invention.

FIG. 8 is a diagram showing a structure to be evaluated of a magnetoresistance effect element according to an embodiment when seen from a direction perpendicular to a stacking direction.

FIG. 9 is a diagram showing the element structure according to the embodiment when seen from the stacking direction.

FIG. 10 is a graph showing results of evaluation of a magnetoresistance effect of a magnetoresistance effect element of Example 1.

FIG. 11 shows results of X-ray diffraction measurement for obtaining a lattice constant regarding an oxidized and nitrided element of Example 8.

FIG. 12 shows results of measurement of a magnetoresistance effect of the oxidized and nitrided element of Example 8 at a bias voltage of 80 mV.

FIG. 13 shows results of measurement of RA of the oxidized and nitrided element of Example 8 at a bias voltage of 80 mV.

FIG. 14 shows results of X-ray diffraction measurement for obtaining a lattice constant regarding an oxidized and nitrided element of Example 9.

FIG. 15 shows results of measurement of a magnetoresistance effect of the oxidized and nitrided element of Example 9 at a bias voltage of 80 mV.

FIG. 16 shows results of measurement of RA of the oxidized and nitrided element of Example 9 at a bias voltage of 80 mV.

FIG. 17 shows results of X-ray diffraction measurement for obtaining a lattice constant regarding an oxidized and nitrided element of Example 10.

FIG. 18 shows results of measurement of a magnetoresistance effect of the oxidized and nitrided element of Example 10 at a bias voltage of 80 mV.

FIG. 19 shows results of measurement of RA of the oxidized and nitrided element of Example 10 at a bias voltage of 80 mV.

FIG. 20 shows results of X-ray diffraction measurement for obtaining a lattice constant regarding an oxidized and fluorinated element of Example 11.

FIG. 21 shows results of measurement of a magnetoresistance effect of the oxidized and fluorinated element of Example 11 at a bias voltage of 80 mV.

FIG. 22 shows results of measurement of RA of the oxidized and fluorinated element of Example 11 at a bias voltage of 80 mV.

FIG. 23 shows an example of a part in which the tunnel barrier layer and the ferromagnetic metal layer are lattice-matched. FIG. 23(A) shows a high-resolution cross-section TEM image. FIG. 23(B) shows an example of an image obtained by performing inverse Fourier analysis.

FIG. 24 is a diagram showing a structure of a cross-section including a direction parallel to a stacking direction of Example 12.

FIG. 25 is a diagram showing a proportion of a lattice-matched portion in which a tunnel barrier layer of Example 12 is lattice-matched with both of a first ferromagnetic metal layer and a second ferromagnetic metal layer, and characteristics of an element. FIG. 25(A) is a diagram showing element resistance (Rp) when magnetization directions of the first ferromagnetic metal layer and the second ferromagnetic metal layer are parallel to each other. FIG. 25(B) is a diagram showing element resistance (Rap) when magnetization directions of the first ferromagnetic metal layer and the second ferromagnetic metal layer are antiparallel to each other. FIG. 25(C) is a diagram showing a magnetoresistance ratio of the element.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference numerals, and an overlapping description thereof will be omitted.

First Embodiment

Hereinafter, a case where a magnetoresistance effect element according to a first embodiment has a first ferromagnetic metal layer 6, a second ferromagnetic metal layer 7, and a tunnel barrier layer 3 sandwiched between the first and second ferromagnetic metal layers, and the tunnel barrier layer 3 has a spinel structure in which cations are disordered, and contains a divalent cation of a non-magnetic element, a trivalent cation of a non-magnetic element, oxygen, and one of nitrogen and fluorine will be described.

(Basic Structure)

In the example shown in FIG. 1, a magnetoresistance effect element 100 is provided on a substrate 1, and has a stacked structure provided with an underlayer 2, a first ferromagnetic metal layer 6, a tunnel barrier layer 3, a second ferromagnetic metal layer 7, and a cap layer 4 in order from the substrate 1.

(Tunnel Barrier Layer)

The tunnel barrier layer 3 is made of a non-magnetic insulating material. In general, the tunnel barrier layer has a film thickness of 3 nm or less, and in a case where the tunnel barrier layer is sandwiched between metal materials, a wave function of electrons of atoms of the metal materials extends beyond the tunnel barrier layer 3, and thus a current may flow regardless of the presence of an insulating material on the circuit. The magnetoresistance effect element 100 is classified into two types including: a type in which the typical tunneling effect is used; and a type in which the coherent tunneling effect where an orbit for tunneling is limited is predominant. In the typical tunneling effect, a magnetoresistance effect is obtained by spin polarization of ferromagnetic materials. On the other hand, in the coherent tunneling, an orbit for tunneling is limited. Therefore, in a magnetoresistance effect element in which coherent tunneling is predominant, an effect higher than or equivalent to spin polarization of ferromagnetic metal materials can be expected. In order to exhibit the coherent tunneling effect, it is necessary that the ferromagnetic metal materials and the tunnel barrier layer 3 be crystallized and joined in a specific orientation.

(Spinel Structure)

FIG. 2 shows a crystal structure of a spinel. An A-site in which oxygen is fourfold coordinated to cations and a B-site in which oxygen is sixfold coordinated to cations exist. Here, a Sukenel structure referring to the spinel structure in which cations are disordered is a structure that has a lattice constant half the lattice constant of an ordered spinel structure while a position of an oxygen atom of the ordered spinel is almost not changed, and in which cations are positioned in tetrahedral positions and octahedral positions of oxygen atoms that are not occupied under ordinary circumstances. At this time, this structure may include total five structures shown in FIGS. 3 to 7, and may be any one of them or a mixed structure thereof.

Definition of Disordered Spinel Structure

In this specification, the spinel structure in which cations are disordered may be referred to as a Sukenel structure. The Sukenel structure refers to a structure where oxygen atoms are arranged in cubic close-packed lattice that is substantially similar to spinel lattice, the structure as a whole belongs to a cubic structure, but arrangement of cations are disordered. In an original ordered spinel, Mg and Al are arranged in order in the tetrahedral vacancies and octahedral vacancies in the original spinel. However, since these are arranged in random arrangement in the Sukenel structure, the crystal symmetry of the structure is different from MgAl₂O₄, and the lattice constant of the structure is substantially half of that of MgAl₂O₄. With a change in the lattice-repeating unit, a combination between the ferromagnetic layer material and the electronic structure (band structure) is changed, and thus a large TMR enhancement due to a coherent tunneling effect is obtained. For example, a space group of MgAl₂O₄ that is a non-magnetic spinel material is Fd-3m, but a space group of a disordered spinel structure with a lattice constant reduced by half is known to be changed to Fm-3m or F-43m, and there are total five structures (Non-Patent Document 2). Any one of them can be used.

In this specification, the Sukenel structure is not essentially required to be a cubic structure. In the stacked structure, the crystal structure is influenced by the crystal structure of the material of an underlayer, and the lattice is thus partially distorted. Each material has a bulk crystal structure, but in a case where it is formed into a thin film, a partially distorted crystal structure based on the bulk crystal structure can be taken. Particularly, in the invention, the tunnel barrier layer has a very thin structure, and is easily influenced by the crystal structure of the layer brought into contact with the tunnel barrier layer. In this regard, the bulk crystal structure of a Sukenel structure is a cubic structure, and in this specification, the Sukenel structure includes a Sukenel structure which does not have a cubic structure in addition to a Sukenel structure slightly deviating from the cubic structure. A deviation from the cubic structure in the Sukenel structure described in this specification is generally slight, and this deviation depends on the accuracy of a measurement method for evaluating the structure.

The divalent cation in the non-magnetic element of the tunnel barrier layer is preferably one or more selected from the group consisting of magnesium, zinc, and cadmium. These non-magnetic elements are stable in a case where the number of valence is 2, and in a case where these non-magnetic elements are constituent elements of the tunnel barrier layer, coherent tunneling can be realized, and the MR ratio is increased.

The trivalent cation in the non-magnetic element of the tunnel barrier layer is preferably one or more selected from the group consisting of aluminum, gallium, and indium. These non-magnetic elements are stable in a case where the number of valence is 3, and in a case where these non-magnetic elements are constituent elements of the tunnel barrier layer, coherent tunneling can be realized, and the MR ratio is increased.

In a case where the trivalent cation contained in the tunnel barrier layer includes a plurality of non-magnetic elements, a difference in ionic radius between the cations is preferably 0.2 Å or less. In a case where the difference in ionic radius is small, the cations are unlikely to be ordered, and thus the lattice constant becomes smaller than that of a general spinel structure. Accordingly, the MR ratio is further increased in a case of two or more types of elements that are similar to each other in ionic radius.

(First Ferromagnetic Metal Layer)

Examples of the material of the first ferromagnetic metal layer 6 include metal selected from the group consisting of Cr, Mn, Co, Fe, and Ni, alloy including one or more of the metals of the group, and alloy including one or more metals selected from the group and at least one element of B, C, and N. Specific examples thereof include Co—Fe and Co—Fe—B. A Heusler alloy such as Co₂FeSi is preferable in order to obtain a high output. The Heusler alloy includes intermetallic compounds having a chemical composition of X₂YZ. X denotes a Co, Fe, Ni, or Cu group transition metal element or noble metal in the periodic table, Y denotes a Mn, V, Cr, or Ti group transition metal, and can also take the elemental species of X, and Z denotes representative elements of III to V groups. Examples thereof include Co₂FeSi, Co₂MnSi, and Co₂Mn_(1-a)Fe_(a)Al_(b)Si_(1-b). In addition, an antiferromagnetic material such as IrMn and PtMn may be used as a material brought into contact with the first ferromagnetic metal layer 6 in order to make coercivity of the first ferromagnetic metal layer larger than that of the second ferromagnetic metal layer 7. Furthermore, the first ferromagnetic metal layer may have a synthetic ferromagnetic coupling structure such that the second ferromagnetic metal layer 7 is not influenced by a leakage magnetic field of the first ferromagnetic metal layer 6.

In a case where a magnetization direction of the first ferromagnetic metal layer 6 is made perpendicular to the stacked plane, a stacked film of Co and Pt is preferably used. For example, in a case where the first ferromagnetic metal layer 6 has a composition of [Co (0.24 nm)/Pt (0.16 nm)]₆/Ru (0.9 nm)/[Pt (0.16 nm)/Co (0.16 nm)]₄/Ta (0.2 nm)/FeB (1.0 nm), the magnetization direction can be made perpendicular to the stacked plane.

(Second Ferromagnetic Metal Layer)

A ferromagnetic material, particularly, a soft magnetic material is applied as a material of the second ferromagnetic metal layer 7, and examples thereof include metal selected from the group consisting of Cr, Mn, Co, Fe, and Ni, alloy including one or more of the metals of the group, and alloy including one or more metals selected from the group and at least one element of B, C, and N. Specific examples thereof include Co—Fe, Co—Fe—B, and Ni—Fe.

In a case where a magnetization direction of the second ferromagnetic metal layer 7 is made perpendicular to the stacked plane, the second ferromagnetic metal layer 7 preferably has a thickness of 2.5 nm or less. Perpendicular magnetic anisotropy can be applied to the second ferromagnetic metal layer 7 at an interface between the second ferromagnetic metal layer 7 and the tunnel barrier layer 3. The second ferromagnetic metal layer 7 preferably has a thin film thickness since the effect of the perpendicular magnetic anisotropy is reduced if the second ferromagnetic metal layer 7 has a thick film thickness.

In general, the first ferromagnetic metal layer 6 has a structure in which the magnetization direction thereof is fixed, and is called a fixed layer. In addition, since the second ferromagnetic metal layer 7 has a magnetization direction that can be more easily changed by an external magnetic field or a spin torque than the first ferromagnetic metal layer 6, the second ferromagnetic metal layer is called a free layer.

(Substrate)

A magnetoresistance effect element according to the invention may be formed on a substrate.

In that case, a material showing excellent flatness is preferably used as a material of the substrate 1. The substrate 1 differs depending on the purpose. For example, in a case of MRAM, a circuit formed in a Si substrate can be used under the magnetoresistance effect element. In a case of a magnetic head, an AlTiC substrate that can be easily processed can be used.

(Underlayer)

In a case where a magnetoresistance effect element according to the invention is formed on a substrate, first, an underlayer may be formed on the substrate.

In that case, the underlayer 2 is used to control crystallinity such as crystal orientation and crystal grain size of the first ferromagnetic metal layer 6 and layers formed above the first ferromagnetic metal layer 6. Therefore, it is important to select the material of the underlayer 2. Hereinafter, the material and the configuration of the underlayer 2 will be described. Any of a conductive material and an insulating material may be used for the underlayer, but in a case where electric power is fed to the underlayer, a conductive material is preferably used. First, as a first example of the underlayer 2, a nitride layer having a (001)-oriented NaCl structure and containing at least one element selected from the group consisting of Ti, Zr, Nb, V, Hf, Ta, Mo, W, B, Al, and Ce is exemplified. As a second example of the underlayer 2, a (002)-oriented perovskite conductive oxide layer made of RTO₃ is exemplified. Here, the R-site includes at least one element selected from the group consisting of Sr, Ce, Dy, La, K, Ca, Na, Pb, and Ba, and the T-site includes at least one element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Nb, Mo, Ru, Ir, Ta, Ce, and Pb. As a third example of the underlayer 2, an oxide layer having a (001)-oriented NaCl structure and containing at least one element selected from the group consisting of Mg, Al, and Ce is exemplified. As a fourth example of the underlayer 2, a layer having a (001)-oriented tetragonal or cubic structure and containing at least one element selected from the group consisting of Al, Cr, Fe, Co, Rh, Pd, Ag, Ir, Pt, Au, Mo, and W is exemplified. As a fifth example of the underlayer 2, a layer having a stacked structure with a combination of two or more of the layers of the above first to fourth examples is exemplified. By devising the structure of the underlayer as described above, it is possible to control the crystallinity of the ferromagnetic layer 2 and layers formed above the ferromagnetic layer 2, thereby improving the magnetic characteristics.

(Cap Layer)

A cap layer may be formed on the second ferromagnetic metal layer of the magnetoresistance effect element according to the invention.

A cap layer 4 is installed above the second ferromagnetic metal layer 7 in a stacking direction in order to control crystallinity such as crystal orientation and crystal grain size and element diffusion. In a case where a free layer having a bcc structure is formed, the crystal structure of the cap layer may be any one of a fcc structure, a hcp structure, and a bcc structure. In a case where a free layer having a fcc structure is formed, the crystal structure of the cap layer may be any one of a fcc structure, a hcp structure, and a bcc structure. The film thickness of the cap layer may be within such a range that a distortion relaxation effect is obtained and a reduction in the MR ratio by shunt is not shown. The film thickness of the cap layer is preferably 1 nm to 30 nm.

(Shape and Dimensions of Element)

A laminate formed of the first ferromagnetic metal layer, the tunnel barrier layer, and the second ferromagnetic metal layer 2 constituting the invention has a columnar shape. In addition, it may have various shapes such as a circular shape, a square shape, a triangle shape, and a polygonal shape when viewed from top, and preferably has a circular shape from the viewpoint of symmetry. That is, the laminate preferably has a columnar shape.

FIGS. 8 and 9 show examples of the shape and the dimensions of the magnetoresistance effect element.

FIG. 8 is a diagram showing a structure when viewed from a side in a stacking direction of the magnetoresistance effect element 100. The magnetoresistance effect element 100 of FIG. 8 has an electrode layer 5 formed above the cap layer 4 shown in FIG. 1. FIG. 9 is a diagram showing a structure when viewed in the stacking direction of the magnetoresistance effect element 100. In FIG. 9, a current source 71 and a voltmeter 72 are also shown.

The magnetoresistance effect element 100 is processed into a columnar shape of 80 nm or less as shown in FIGS. 8 and 9, and wiring is applied. Since the magnetoresistance effect element 100 is processed into a columnar shape having a size of 80 nm or less, a domain structure is not likely to be formed in the ferromagnetic metal layers, and it is not necessary to consider a component having a different spin polarization in the ferromagnetic metal layers In FIG. 9, the magnetoresistance effect element 100 is disposed at a position where the underlayer 2 and the electrode layer 5 intersect each other.

(Evaluation Method)

The magnetoresistance effect element 100 can be evaluated with the structure shown in FIGS. 8 and 9. For example, the power supply 71 and the voltmeter 72 are disposed as shown in FIG. 9 such that a fixed current or a fixed voltage is applied to the magnetoresistance effect element 100. By measuring the voltage or the current while sweeping an external magnetic field, a change in the resistance of the magnetoresistance effect element 100 can be measured.

In general, the MR ratio is expressed by the following formula.

MR Ratio (%)={(R _(AP) −R _(P))/R _(P)}×100

R_(P) denotes a resistance in a case where magnetization directions of the first ferromagnetic metal layer 6 and the second ferromagnetic metal 7 are parallel to each other, and R_(AP) denotes a resistance in a case where magnetization directions of the first ferromagnetic metal layer 6 and the second ferromagnetic metal 7 are antiparallel to each other.

In a case where a strong current flows in the magnetoresistance effect element 100, magnetization rotation occurs by a STT effect, and a resistance value of the magnetoresistance effect element 100 is rapidly changed. The current value at which the resistance value is rapidly changed is called an inversion current value (Jc).

(Others)

In this embodiment, the structure has been exemplified in which the first ferromagnetic metal layer 6 having high coercivity is disposed on the lower side, but the invention is not limited to this structure. In a case of a structure in which the first ferromagnetic metal layer 6 having high coercivity is disposed on the upper side, the coercivity is reduced in comparison with a case in which the first ferromagnetic metal layer 6 is disposed on the lower side, but the tunnel barrier layer 3 can be formed by utilizing the crystallinity of the substrate, and thus the MR ratio can be increased.

In order to utilize the magnetoresistance effect element as a magnetic sensor, a resistance change preferably changes linearly with respect to an external magnetic field. In a general laminated film of ferromagnetic layers, magnetization directions are easily directed into the lamination plane by shape anisotropy. In this case, for example, a magnetic field is applied from outside to make the magnetization directions of the first ferromagnetic metal layer and the second ferromagnetic metal layer intersect each other, thereby changing the resistance change linearly with respect to the external magnetic field. However, in this case, since a mechanism that applies a magnetic field is required near the magnetoresistance effect element, this is not preferable for integration. In a case where the ferromagnetic metal layer itself has perpendicular magnetic anisotropy, this is advantageous for integration since a method such as application of a magnetic field from outside is not required.

The magnetoresistance effect element using this embodiment can be used as a magnetic sensor or a memory such as a MRAM. Particularly, this embodiment is effective for products that are used with a bias voltage higher than a bias voltage used in conventional magnetic sensors.

(Manufacturing Method)

The magnetoresistance effect element 100 can be formed using, for example, a magnetron sputtering apparatus.

The tunnel barrier layer 3 can be produced through a known method. For example, a thin metal film is formed on the first ferromagnetic metal layer 6 by sputtering, performing plasma oxidation or natural oxidation by oxygen introduction thereon, and performing a heat treatment thereon. As the film-forming method, not only a magnetron sputtering method but also a thin film-forming method such as a vapor deposition method, a laser ablation method, or a MBE method can be used.

Each of the underlayer, the first ferromagnetic metal layer, the second ferromagnetic metal layer, and the cap layer can be formed through a known method.

(Tunnel Barrier Layer Evaluation Method)

Structure analysis of the tunnel barrier layer 3 was evaluated with an electron diffraction image obtained using a transmission electron microscope. The structure of the barrier layer is examined through this method, and it is possible to discriminate whether the structure is a spinel structure or a Sukenel structure by the presence or absence of reflection from the {022} plane and the {111} plane shown in the ordered spinel structure. In addition, a lattice constant of the tunnel barrier layer 3 was obtained from an electron beam diffraction image. The lattice constant and the configuration ratio between nitrogen and oxygen can be obtained by forming a thick film of the tunnel barrier layer 3 through the same method as in examples and by evaluating the film. The lattice constant can be obtained with high accuracy using X-ray diffraction. In addition, an oxygen and nitrogen analyzer was used for composition analysis. In this embodiment, the tunnel barrier layer 3 is chemically stable and has resistance to a chemical treatment and mechanical abrasion. For example, the substrate of the produced thick film is removed by mechanical abrasion, and the metal film remaining on the tunnel barrier layer 3 can be removed by a chemical treatment. The sample consisting of only of the tunnel barrier layer 3 is put into a graphite crucible, and melted by heating it in a He atmosphere. Oxygen in the sample reacts with the graphite crucible, and carbon monoxide is generated. Carbon monoxide is oxidized to carbon dioxide, and the concentration thereof is analyzed using an infrared detector. Of nitrogen, carbon dioxide and moisture generated through heating and melting, carbon dioxide and moisture are absorbed and separated from nitrogen, the concentration of the remaining nitrogen is measured using a thermal conductivity detector, and thus the oxygen content and the nitrogen content can be specified.

Second Embodiment

A second embodiment is different from the first embodiment only in the method of forming a tunnel barrier layer. In the first embodiment, the tunnel barrier layer is formed by repeatedly performing formation and oxidation of a metal film. In the second embodiment, the substrate temperature is lowered to −70 to −30 degrees, and then oxidation is performed in the oxidation step. By cooling the substrate, a temperature gradient is generated between the substrate and the vacuum or between the substrate and the plasma. First, in a case where a surface of the substrate is exposed to oxygen, oxygen reacts with the metal material and the metal material is oxidized. However, the oxidation does not proceed due to the low temperature. Accordingly, the oxygen amount of the tunnel barrier layer is easily adjusted. Moreover, by forming the temperature gradient, epitaxial growth (lattice-matched growth) is easily adjusted. Since the crystal growth proceeds by the temperature gradient, the epitaxial growth is easily performed in a case where the temperature of the substrate is sufficiently lowered. As the temperature of the substrate is increased, domains are formed and a plurality of crystal nuclei are thus formed in the plane. Each of the crystal nuclei is independently and epitaxially grown, and thus a part in which lattices are not matched is formed in a part in which the grown domains are in contact with each other.

It is preferable that in the tunnel barrier layer, lattice-matched; parts, which are lattice-matched with both of a first ferromagnetic metal layer and a second ferromagnetic metal layer, partially exist. In general, it is preferable that the tunnel barrier layer be completely lattice-matched to both of the first ferromagnetic metal layer and the second ferromagnetic metal layer. However, in a case where the tunnel barrier layer is completely lattice-matched, spin-polarized electrons interfere with each other during passing through the tunnel barrier layer, and thus the electrons do not easily pass through the tunnel barrier layer. In contrast, in a case where lattice-matched parts, in which lattices are matched, partially exist, the interference between spin-polarized electrons during passing through the tunnel barrier layer is appropriately cut in parts in which lattices are not matched, and thus the spin-polarized electrons easily pass through the tunnel barrier layer. The volume ratio of the lattice-matched part portion in the tunnel barrier layer with respect to the volume of the entire tunnel barrier layer is preferably 65% to 95%. In a case where the volume ratio of the lattice-matched part in the tunnel barrier layer is 65% or less, the effect of coherent tunneling is reduced, and thus the MR ratio decreases. In a case where the volume ratio of the lattice-matched part in the tunnel barrier layer is 95% or greater, the interference effect between the spin-polarized electrons during passing through the tunnel barrier layer is not be weakened, and thus an increase in passage of the spin-polarized electrons through the tunnel barrier layer is not observed.

(Method of Calculating Volume Ratio of Lattice-Matched Portion)

The volume ratio of the lattice-matched part (lattice-matched portion) with respect to the volume of the entire tunnel barrier layer can be estimated from, for example, a TEM image. Regarding whether the lattices are matched, a part including the tunnel barrier layer, the first ferromagnetic metal layer, and the second ferromagnetic metal layer in a cross-section TEM image is Fourier-transformed to obtain an electron beam diffraction image. In the electron beam diffraction image obtained by Fourier transformation, electron beam diffraction spots in directions other than the stacking direction are removed. That image is subjected to inverse Fourier transformation to provide an image in which information only in the stacking direction is obtained. In lattice lines in the inverse Fourier image, a part in which the tunnel barrier layer is continuously connected to both of the first ferromagnetic metal layer and the second ferromagnetic metal layer is defined as a lattice-matched portion. In addition, in lattice lines, a part in which the tunnel barrier layer is not continuously connected to at least one of the first ferromagnetic metal layer and the second ferromagnetic metal layer, or in which no lattice lines are detected, is defined as a lattice-mismatched portion. In the lattice-matched portion, in the lattice lines in the inverse Fourier image, the layers are continuously connected from the first ferromagnetic metal layer to the second ferromagnetic metal layer via the tunnel barrier layer, and thus a width (L_(C)) of the lattice-matched portion can be measured from the TEM image. Similarly, in the lattice-mismatched portion, in the lattice lines in the inverse Fourier image, the layers are not continuously connected, and thus a width (L_(I)) of the lattice-mismatched portion can be measured from the TEM image. Using the width (L_(C)) of the lattice-matched portion as a numerator and using the sum of the width (L_(C)) of the lattice-matched portion and the width (L_(I)) of the lattice-mismatched portion as a denominator, the volume ratio of the lattice-matched portion with respect to the volume of the entire tunnel barrier layer can be obtained. The TEM image is a cross-section image, but includes information including a depth. Accordingly, it can be thought that the region estimated from the TEM image is proportional to the volume.

FIG. 23 shows an example of the part in which the tunnel barrier layer and the ferromagnetic metal layer are lattice-matched. FIG. 23(A) shows an example of a high-resolution cross-section TEM image. FIG. 23(B) shows an example of an image obtained by performing inverse Fourier transformation after removal of electron beam diffraction spots in directions other than the stacking direction in the electron beam diffraction image. In FIG. 23(B), components perpendicular to the stacking direction are removed, and thus lattice lines can be observed in the stacking direction. This shows that the tunnel barrier layer and the ferromagnetic metal layer are continuously connected to each other without interruption at an interface therebetween.

EXAMPLES Example 1

Hereinafter, an example of the method of manufacturing a magnetoresistance effect element according to the first embodiment will be described. Film formation was performed on a substrate provided with a thermal silicon oxide film using a magnetron sputtering method. As an underlayer, 5 nm of Ta/3 nm of Ru was formed, and as a first ferromagnetic metal layer, 12 nm of IrMn/10 nm of CoFe/0.8 nm of Ru/7 nm of CoFe was formed in this order on the underlayer.

Next, a method of forming a tunnel barrier layer will be shown. A 0.6 nm thick film of Mg_(0.9)Al₂ is formed by sputtering with a target having an alloy composition of Mg_(0.9)Al₂. Thereafter, the above-described sample was moved to an oxidation chamber of which the inside was kept in an ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidation by introducing Ar, oxygen, and nitrogen in a state in which the substrate was heated at 250° C. First, plasma nitridation was performed for 1 minute at a partial pressure ratio of 1:25 (Ar:nitrogen) and a total gas pressure of 1 Pa. Then, after waiting until the pressure inside the oxidation chamber was equal to or less than an ultrahigh vacuum of 1×10⁻⁸ Pa or less, natural oxidation was performed for 20 seconds at a partial pressure ratio of 1:25:5 (Ar:oxygen:nitrogen) and a total gas pressure of 0.05 Pa. Then, the sample was returned to a film-forming chamber, and a film of Mg_(0.9)Al₂ with a thickness of 0.5 nm was formed. The above-described sample was moved to the oxidation chamber of which the inside was kept in an ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidation and inductively coupled plasma oxidation by introducing Ar and oxygen. The natural oxidation time was 30 seconds, and the inductively coupled plasma oxidation time was 5 seconds. The partial pressure ratio of Ar to oxygen was 1 to 20, and the total gas pressure was 0.08 Pa.

In this example, the above-described method was repeated 1,000 times to form a tunnel barrier layer having a thickness of 1.1 μm in order to perform the evaluation of the tunnel barrier layer. In this example, regarding the tunnel barrier layer having a thickness of 1.1 μm, it was judged that a film that was the same as the tunnel barrier layer of a magnetoresistance effect element was formed.

The above-described lamination film was moved again to the film-forming chamber, and a 5 nm CoFe film was formed as a second ferromagnetic metal layer 7. 3 nm of Ru/5 nm of Ta was formed as a cap layer 4.

The above-described stacked film was installed in an annealing apparatus, and was heated at a temperature of 450° C. in an Ar atmosphere for 10 minutes. Thereafter, under an applied field of 8 kOe, a heat treatment was performed on the stacked film at 280 degrees for 6 hours.

Next, an element was formed as in FIG. 9. First, a photoresist was formed using electron beam lithography in such a way that the electrode layer was in a direction rotated by 90 degrees as in FIG. 9. A part other than a part below the photoresist was eliminated by an ion milling method to expose the thermal silicon oxide film that was the substrate, and thus a shape of the underlayer 2 was formed. In a narrow part in the shape of the underlayer, a photoresist was formed into a cylindrical shape of 80 nm using electron beam lithography, and a part other than a part below the photoresist was eliminated by an ion milling method to expose the underlayer. Thereater, SiOx was formed as an insulating layer on the part shaved by ion milling. Here, the photoresist with a cylindrical shape of 80 nm was removed. The photoresist was not formed only in a part corresponding to an electrode pad of FIG. 9, and the insulating layer was removed by an ion milling method to expose the underlayer. Thereafter, an Au layer was formed. This electrode pad 8 functions as a contact electrode for the underlayer of the above-described stacked film. Next, a photoresist was formed and shaping was performed by an ion milling method such that the electrode layer of FIG. 9 was formed, and an Au film was formed. This functions as a contact electrode for the electrode layer of the above-described stacked film.

(Characteristic Evaluation of Example 1)

The magnetoresistance effect element evaluation method is based on a magnetoresistance effect element evaluation method that has been generally performed. As shown in FIG. 9, a current source and a voltmeter were connected to the electrode pad and the electrode layer, respectively, to perform measurement by a four-terminal method. 80 mV of a bias voltage was applied from the voltmeter, and a current was measured by the current source to obtain a resistance value. The changing resistance value was observed by applying a magnetic field to the magnetoresistance effect element from outside. FIG. 10 is a diagram showing results of the evaluation of the magnetoresistance effect of the magnetoresistance effect element of Example 1. The horizontal axis represents a magnetic field, and the vertical axis represents the resistance of the element. The bias voltage applied was 80 mV, and electrons flowed in a direction from the first ferromagnetic metal layer to the second ferromagnetic layer 7. From FIG. 10, it was found that the MR ratio was 166%, and the area resistance (RA) of the element was 0.43 Ω·μm².

(Structure Analysis of Example 1)

Structure analysis of the tunnel barrier layer was evaluated with an electron diffraction image obtained using a transmission electron microscope. The structure of the barrier layer was examined through this method, and it was confirmed that there was no reflection from the {022} plane and the {111} plane shown in the ordered spinel structure. In addition, it was found that this barrier had a cubic structure in which the spinel structure was disordered.

(Composition Analysis of Example 1)

The composition of the tunnel barrier layer having a thickness of 1.1 μm was analyzed using an oxygen and nitrogen analyzer. The substrate of the produced tunnel barrier layer having a thickness of 1.1 μm was removed by mechanical abrasion, and the metal film remaining on the tunnel barrier layer was removed by a chemical treatment. The sample consisting of only of the tunnel barrier layer 3 was put into a graphite crucible, and melted by heating it in a He atmosphere. Oxygen in the sample reacted with the graphite crucible, and carbon monoxide was generated. Carbon monoxide was oxidized to carbon dioxide, and the concentration thereof was analyzed using an infrared detector. Of nitrogen, carbon dioxide and moisture generated through heating and melting, carbon dioxide and moisture were absorbed and separated from nitrogen, the concentration of the remaining nitrogen was measured using a thermal conductivity detector, and thus the oxygen content and the nitrogen content could be specified. As a standard of the composition ratio, the sum of the oxygen content and the nitrogen content was defined as 1, and relative amounts of oxygen and nitrogen were compared to each other. As a result, O:N=0.97:0.03 was obtained.

Example 2

The production method is similar to that in the Example 1, but only the material for forming the tunnel barrier layer is different from that of Example 1. A 0.6 nm thick film of Mg_(0.9)Al₂ is formed by sputtering with a target having an alloy composition of Mg_(0.9)Al₂. Thereafter, the above-described sample was moved to an oxidation chamber of which the inside was kept in an ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidation by introducing Ar, oxygen, and fluorine in a state in which the substrate was heated at 250° C. First, natural fluorination was performed for 1 minute at a partial pressure ratio of 1:25 (fluorine:Ar) and a total gas pressure of 0.01 Pa. Then, after waiting until the pressure inside the oxidation chamber was equal to or less than an ultrahigh vacuum of 1×10⁻⁸ Pa or less, natural oxidation was performed for 20 seconds at a partial pressure ratio of 1:25:0.1 (Ar:oxygen:fluorine) and a total gas pressure of 0.05 Pa. Then, the sample was returned to a film-forming chamber, and a film of Mg_(0.9)Al₂ with a thickness of 0.5 nm was formed. The above-described sample was moved to the oxidation chamber of which the inside was kept in an ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidation and inductively coupled plasma oxidation by introducing Ar and oxygen. The natural oxidation time was 30 seconds, and the inductively coupled plasma oxidation time was 5 seconds. The partial pressure ratio of Ar to oxygen was 1 to 20, and the total gas pressure was 0.08 Pa.

(Characteristics of Example 2)

As a result of the measurement of the magnetoresistance effect, it was found that in a case where the bias voltage was 80 mV, the MR ratio was 148%, and the area resistance (RA) of the element was 0.5 Ω·μm². A cubic structure in which the spinel structure was disordered was confirmed from an electron beam diffraction image. The composition of the tunnel barrier layer having a thickness of 1.1 μm was analyzed using an oxygen and nitrogen analyzer, and as a result, as a standard of the composition ratio, the sum of the oxygen content and the fluorine content was defined as 1, and relative amounts of oxygen and fluorine were compared to each other. As a result, O:F=0.98:0.02 was obtained.

Example 3

The production method is similar to that in the Example 1, but only the material for forming the tunnel barrier layer is different from that of Example 1 Å 0.6 nm thick film of Zn_(0.9)Al₂ is formed by sputtering with a target having an alloy composition of Zn_(0.9)Al₂. Thereafter, the above-described sample was moved to an oxidation chamber of which the inside was kept in an ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidation by introducing Ar, oxygen, and nitrogen in a state in which the substrate was heated at 250° C. First, plasma nitridation was performed for 1 minute at a partial pressure ratio of 1:25 (Ar:nitrogen) and a total gas pressure of 1 Pa. Then, after waiting until the pressure inside the oxidation chamber was equal to or less than an ultrahigh vacuum of 1×10⁻⁸ Pa or less, natural oxidation was performed for 20 seconds at a partial pressure ratio of 1:25:5 (Ar:oxygen:nitrogen) and a total gas pressure of 0.05 Pa. Then, the sample was returned to a film-forming chamber, and a film of Zn_(0.9)Al₂ with a thickness of 0.5 nm was formed. The above-described sample was moved to the oxidation chamber of which the inside was kept in an ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidation and inductively coupled plasma oxidation by introducing Ar and oxygen. The natural oxidation time was 30 seconds, and the inductively coupled plasma oxidation time was 5 seconds. The partial pressure ratio of Ar to oxygen was 1 to 20, and the total gas pressure was 0.08 Pa.

(Characteristics of Example 3)

As a result of the measurement of the magnetoresistance effect, it was found that in a case where the bias voltage was 80 mV, the MR ratio was 142%, and the area resistance (RA) of the element was 0.44 Ω·μm². A cubic structure in which the spinel structure was disordered was confirmed from an electron beam diffraction image. The composition of the tunnel barrier layer having a thickness of 1.1 μm was analyzed using an oxygen and nitrogen analyzer, and as a result, as a standard of the composition ratio, the sum of the oxygen content and the nitrogen content was defined as 1, and relative amounts of oxygen and fluorine were compared to each other. As a result, O:N=0.97:0.03 was obtained.

Example 4

The production method is similar to that in the Example 1, but only the material for forming the tunnel barrier layer is different from that of Example 1 Å 0.6 nm thick film of Mg_(0.9)Ga₂ is formed by sputtering with a target having an alloy composition of Mg_(0.9)Ga₂. Thereafter, the above-described sample was moved to an oxidation chamber of which the inside was kept in an ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidation by introducing Ar, oxygen, and nitrogen in a state in which the substrate was heated at 250° C. First, plasma nitridation was performed for 1 minute at a partial pressure ratio of 1:25 (Ar:nitrogen) and a total gas pressure of 1 Pa. Then, after waiting until the pressure inside the oxidation chamber was equal to or less than an ultrahigh vacuum of 1×10⁻⁸ Pa or less, natural oxidation was performed for 20 seconds at a partial pressure ratio of 1:25:5 (Ar:oxygen:nitrogen) and a total gas pressure of 0.05 Pa. Then, the sample was returned to a film-forming chamber, and a film of Mg_(0.9)Ga₂ with a thickness of 0.5 nm was formed. The above-described sample was moved to the oxidation chamber of which the inside was kept in an ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidation and inductively coupled plasma oxidation by introducing Ar and oxygen. The natural oxidation time was 30 seconds, and the inductively coupled plasma oxidation time was 5 seconds. The partial pressure ratio of Ar to oxygen was 1 to 20, and the total gas pressure was 0.08 Pa.

(Characteristics of Example 4)

As a result of the measurement of the magnetoresistance effect, it was found that in a case where the bias voltage was 80 mV, the MR ratio was 125%, and the area resistance (RA) of the element was 0.39 Ω·μm². A cubic structure in which the spinel structure was disordered was confirmed from an electron beam diffraction image. The composition of the tunnel barrier layer having a thickness of 1.1 μm was analyzed using an oxygen and nitrogen analyzer, and as a result, as a standard of the composition ratio, the sum of the oxygen content and the nitrogen content was defined as 1, and relative amounts of oxygen and fluorine were compared to each other. As a result, O:N=0.97:0.03 was obtained.

Example 5

The production method is similar to that in the Example 1, but only the material for forming the tunnel barrier layer is different from that of Example 1 Å 0.6 nm thick film of Mg_(0.9)In₂ is formed by sputtering with a target having an alloy composition of Mg_(0.9)In₂. A target having an alloy composition of Mg_(0.9)In₂ was subjected to sputtering to form a film of Mg_(0.9)Ga₂ with a thickness of 0.6 nm. Thereafter, the above-described sample was moved to an oxidation chamber of which the inside was kept in an ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidation by introducing Ar, oxygen, and nitrogen in a state in which the substrate was heated at 250° C. First, plasma nitridation was performed for 1 minute at a partial pressure ratio of 1:25 (Ar:nitrogen) and a total gas pressure of 1 Pa. Then, after waiting until the pressure inside the oxidation chamber was equal to or less than an ultrahigh vacuum of 1×10⁻⁸ Pa or less, natural oxidation was performed for 20 seconds at a partial pressure ratio of 1:25:5 (Ar:oxygen:nitrogen) and a total gas pressure of 0.05 Pa. Then, the sample was returned to a film-forming chamber, and a film of Mg_(0.9)In₂ with a thickness of 0.5 nm was formed. The above-described sample was moved to the oxidation chamber of which the inside was kept in an ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidation and inductively coupled plasma oxidation by introducing Ar and oxygen. The natural oxidation time was 30 seconds, and the inductively coupled plasma oxidation time was 5 seconds. The partial pressure ratio of Ar to oxygen was 1 to 20, and the total gas pressure was 0.08 Pa.

(Characteristics of Example 5)

As a result of the measurement of the magnetoresistance effect, it was found that in a case where the bias voltage was 80 mV, the MR ratio was 86%, and the area resistance (RA) of the element was 0.15 Ω·μm². A cubic structure in which the spinel structure was disordered was confirmed from an electron beam diffraction image. The composition of the tunnel barrier layer having a thickness of 1.1 μm was analyzed using an oxygen and nitrogen analyzer, and as a result, as a standard of the composition ratio, the sum of the oxygen content and the nitrogen content was defined as 1, and relative amounts of oxygen and fluorine were compared to each other. As a result, O:N=0.97:0.03 was obtained.

Example 6

The production method is similar to that in the Example 1, but only the material for forming the tunnel barrier layer is different from that of Example 1 Å 0.6 nm thick film of Mg_(0.5)Zn_(0.4)Al₂ is formed by sputtering with a target having an alloy composition of Mg_(0.5)Zn_(0.4)Al₂. Thereafter, the above-described sample was moved to an oxidation chamber of which the inside was kept in an ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidation by introducing Ar, oxygen, and nitrogen in a state in which the substrate was heated at 250° C. First, plasma nitridation was performed for 1 minute at a partial pressure ratio of 1:25 (Ar:nitrogen) and a total gas pressure of 1 Pa. Then, after waiting until the pressure inside the oxidation chamber was equal to or less than an ultrahigh vacuum of 1×10⁻⁸ Pa or less, natural oxidation was performed for 20 seconds at a partial pressure ratio of 1:25:5 (Ar:oxygen:nitrogen) and a total gas pressure of 0.05 Pa. Then, the sample was returned to a film-forming chamber, and a film of Mg_(0.5)Zn_(0.4)Al₂ with a thickness of 0.5 nm was formed. The above-described sample was moved to the oxidation chamber of which the inside was kept in an ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidation and inductively coupled plasma oxidation by introducing Ar and oxygen. The natural oxidation time was 30 seconds, and the inductively coupled plasma oxidation time was 5 seconds. The partial pressure ratio of Ar to oxygen was 1 to 20, and the total gas pressure was 0.08 Pa.

(Characteristics of Example 6)

As a result of the measurement of the magnetoresistance effect, it was found that in a case where the bias voltage was 80 mV, the MR ratio was 177%, and the area resistance (RA) of the element was 0.41 Ω·μm². A cubic structure in which the spinel structure was disordered was confirmed from an electron beam diffraction image. The composition of the tunnel barrier layer having a thickness of 1.1 μm was analyzed using an oxygen and nitrogen analyzer, and as a result, as a standard of the composition ratio, the sum of the oxygen content and the nitrogen content was defined as 1, and relative amounts of oxygen and fluorine were compared to each other. As a result, O:N=0.97:0.03 was obtained.

Example 7

The production method is similar to that in the Example 1, but only the material for forming the tunnel barrier layer is different from that of Example 1 Å 0.6 nm thick film of Mg_(0.9)Al_(1.3)Ga_(0.7) is formed by sputtering with a target having an alloy composition of Mg_(0.9)Al_(1.3)Ga_(0.7). Thereafter, the above-described sample was moved to an oxidation chamber of which the inside was kept in an ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidation by introducing Ar, oxygen, and nitrogen in a state in which the substrate was heated at 250° C. First, plasma nitridation was performed for 1 minute at a partial pressure ratio of 1:25 (Ar:nitrogen) and a total gas pressure of 1 Pa. Then, after waiting until the pressure inside the oxidation chamber was equal to or less than an ultrahigh vacuum of 1×10⁻⁸ Pa or less, natural oxidation was performed for 20 seconds at a partial pressure ratio of 1:25:5 (Ar:oxygen:nitrogen) and a total gas pressure of 0.05 Pa. Then, the sample was returned to a film-forming chamber, and a film of Mg_(0.9)Al_(1.3)Ga_(0.7) with a thickness of 0.5 nm was formed. The above-described sample was moved to the oxidation chamber of which the inside was kept in an ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidation and inductively coupled plasma oxidation by introducing Ar and oxygen. The natural oxidation time was 30 seconds, and the inductively coupled plasma oxidation time was 5 seconds. The partial pressure ratio of Ar to oxygen was 1 to 20, and the total gas pressure was 0.08 Pa.

(Characteristics of Example 7)

As a result of the measurement of the magnetoresistance effect, it was found that in a case where the bias voltage was 80 mV, the MR ratio was 152%, and the area resistance (RA) of the element was 0.45 Ω·μm². A cubic structure in which the spinel structure was disordered was confirmed from an electron beam diffraction image. The composition of the tunnel barrier layer having a thickness of 1.1 μm was analyzed using an oxygen and nitrogen analyzer, and as a result, as a standard of the composition ratio, the sum of the oxygen content and the nitrogen content was defined as 1, and relative amounts of oxygen and fluorine were compared to each other. As a result, O:N=0.97:0.03 was obtained.

Example 8

The production method is similar to that in the Example 1, but only the material for forming the tunnel barrier layer is different from that of Example 1 Particularly, the nitridation and oxidation process performed after the first Mg_(0.9)Al₂ film formation and the second Mg_(0.9)Al₂ film formation is different. A 0.6 nm thick film of Mg_(0.9)Al₂ is formed by sputtering with a target having an alloy composition of Mg_(0.9)Al₂. Thereafter, the above-described sample was moved to an oxidation chamber of which the inside was kept in an ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidation by introducing Ar, oxygen, and nitrogen in a state in which the substrate was heated at 250° C. First, plasma nitridation was performed for 1 minute at a partial pressure ratio of 1:10 to 50 (Ar:nitrogen) and a total gas pressure of 1 Pa. Then, after waiting until the pressure inside the oxidation chamber was equal to or less than an ultrahigh vacuum of 1×10⁻⁸ Pa or less, natural oxidation was performed for 5 to 300 seconds at a partial pressure ratio of 1:25:5 (Ar:oxygen:nitrogen) and a total gas pressure of 0.05 Pa. Then, the sample was returned to a film-forming chamber, and a film of Mg_(0.9)Al₂ with a thickness of 0.5 nm was formed. The above-described sample was moved to the oxidation chamber of which the inside was kept in an ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidation and inductively coupled plasma oxidation by introducing Ar and oxygen. The natural oxidation time was 30 seconds, and the inductively coupled plasma oxidation time was 5 seconds. The partial pressure ratio of Ar to oxygen was 1:5 to 30, and the total gas pressure was 0.08 Pa. The ratio between the oxygen amount and the nitrogen amount in the tunnel barrier layer is determined by the degree of the nitridation of the first nitridation and oxidation process and the degree of the second oxidation. Particularly, in a case where the degree of the second oxidation is increased, the nitridation amount can be adjusted to some extent by the second oxidation even in a case where the amount of the first nitridation is large. In this case, since the degree of the oxidation of the tunnel barrier layer is increased, it is necessary to previously reduce the degree of the first oxidation.

A cubic structure in which the spinel structure was disordered was confirmed from an electron beam diffraction image. The composition of the tunnel barrier layer having a thickness of 1.1 μm was analyzed using an oxygen and nitrogen analyzer, and as a result, as a standard of the composition ratio, the sum of the oxygen content and the nitrogen content was defined as 1, and relative amounts of oxygen and fluorine were compared to each other. The lattice constant of the tunnel barrier layer was obtained using X-ray diffraction measurement.

FIG. 11 shows results of the X-ray diffraction measurement for obtaining the lattice constant regarding the oxidized and nitrided element. The lattice constant linearly changes at a nitrogen content of up to approximately 3.5%, and can be thought to change as an effect of the introduction of the nitrogen to the crystal lattice. In addition, the fact that the lattice constant changes even in a case where the nitrogen content is 8% indicates that the tunnel barrier layer of Example 8 may contain at least 8% of nitrogen.

FIG. 12 shows results of the measurement of the magnetoresistance effect of the oxidized and nitrided element at a bias voltage of 80 mV. The horizontal axis represents the nitrogen amount in anions obtained by an oxygen and nitrogen analyzer, and the vertical axis represents the MR ratio. A peak shape is shown in which the MR ratio is increased at any nitrogen content in comparison with a case where the nitrogen content is zero and the maximum MR ratio peak appears at a nitrogen content of 2%. That is, it is found that nitrogen is preferably contained for improving the MR ratio of the tunnel barrier layer. In addition, it is found that the nitrogen content is more preferably at least 0.5% to 3.5% based on the half value width of the peak shape of FIG. 12.

FIG. 13 shows results of the measurement of RA of the oxidized and nitrided element at a bias voltage of 80 mV. It is found that the RA is rapidly reduced by introducing just a slight amount of nitrogen to the tunnel barrier layer. This indicates that the level of the nitrogen or fluorine partially substituted with oxygen functions and a bandgap narrowing effect is made. In addition, there is a tendency that the value of the RA is minimum at a nitrogen content of 2%, and the RA is increased again at a nitrogen content exceeding 2%. This indicates that the nitrogen introduced excessively functions as a scatterer of conduction. It is found that nitrogen is preferably contained for reducing the RA of the tunnel barrier layer. In addition, it is found that the nitrogen content is more preferably at least 0.5% to 3.5% based on the half value width of the peak shape of FIG. 13.

From the above evaluation, it is found that at least the nitrogen is contained in an amount of up to 8% of the anion content in the tunnel barrier layer, and in a region where the nitrogen content is 8% or less of the anion content, any nitrogen content contributes to an increase in the MR ratio and a reduction in the RA, in comparison with a case of a tunnel barrier containing no nitrogen.

Example 9

The production method is similar to that in the Example 8, but only the material for forming the tunnel barrier layer is different from that of Example 8 Particularly, the nitridation and oxidation process performed after the first Al film formation and second Al film formation is different. A 0.6 nm thick Al film is formed by sputtering with a Al target. Thereafter, the above-described sample was moved to an oxidation chamber of which the inside was kept in an ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidation by introducing Ar, oxygen, and nitrogen in a state in which the substrate was heated at 250° C. First, plasma nitridation was performed for 1 minute at a partial pressure ratio of 1:5 to 30 (Ar:nitrogen) and a total gas pressure of 0.5 Pa. Then, after waiting until the pressure inside the oxidation chamber was equal to or less than an ultrahigh vacuum of 1×10⁻⁸ Pa or less, natural oxidation was performed for 5 to 300 seconds at a partial pressure ratio of 1:15:5 (Ar:oxygen:nitrogen) and a total gas pressure of 0.05 Pa. Then, the sample was returned to a film-forming chamber, and a film of Al with a thickness of 0.5 nm was formed. The above-described sample was moved to the oxidation chamber of which the inside was kept in an ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidation and inductively coupled plasma oxidation by introducing Ar and oxygen. The natural oxidation time was 30 seconds, and the inductively coupled plasma oxidation time was 5 seconds. The partial pressure ratio of Ar to oxygen was 1:2 to 20, and the total gas pressure was 0.05 Pa.

A cubic structure in which the spinel structure was disordered was confirmed from an electron beam diffraction image. The composition of the tunnel barrier layer having a thickness of 1.1 μm was analyzed using an oxygen and nitrogen analyzer, and as a result, as a standard of the composition ratio, the sum of the oxygen content and the nitrogen content was defined as 1, and relative amounts of oxygen and fluorine were compared to each other. The lattice constant of the tunnel barrier layer was obtained using X-ray diffraction measurement.

FIG. 14 shows results of the X-ray diffraction measurement for obtaining the lattice constant regarding the oxidized and nitrided element. The lattice constant linearly changes at a nitrogen content of up to approximately 2%, and can be thought to change as an effect of the introduction of the nitrogen to the crystal lattice. In addition, the fact that the lattice constant changes even in a case where the nitrogen content is 8% indicates that the tunnel barrier layer of Example 9 may contain at least 8% of nitrogen.

FIG. 15 shows results of the measurement of the magnetoresistance effect of the oxidized and nitrided element at a bias voltage of 80 mV. The horizontal axis represents the nitrogen amount in anions obtained by an oxygen and nitrogen analyzer, and the vertical axis represents the MR ratio. A peak shape is shown in which the MR ratio is increased at any nitrogen content in comparison with a case where the nitrogen content is zero, and the maximum MR ratio peak appears at a nitrogen content of 1.4%. That is, it is found that nitrogen is preferably contained for improving the MR ratio of the tunnel barrier layer. In addition, it is found that the nitrogen content is more preferably at least 0.5% to 3.5% based on the half value width of the peak shape of FIG. 15.

FIG. 16 shows results of the measurement of RA of the oxidized and nitrided element at a bias voltage of 80 mV. It is found that the RA is rapidly reduced by introducing just a slight amount of nitrogen to the tunnel barrier layer. This indicates that the level of the nitrogen or fluorine partially substituted with oxygen functions, and a bandgap narrowing effect is made. In addition, there is a tendency that the value of the RA is minimum at a nitrogen content of 1%, and the RA is increased again at a nitrogen content exceeding 1%. This indicates that the nitrogen introduced excessively functions as a scatterer of conduction. It is found that nitrogen is preferably contained for reducing the RA of the tunnel barrier layer. In addition, it is found that the nitrogen content is more preferably at least 0.3% to 2% based on the half value width of the peak shape of FIG. 16.

From the above evaluation, it is found that at least the nitrogen is contained in an amount of up to 8% of the anion content in the tunnel barrier layer, and in a region where the nitrogen content is 8% or less of the anion content, any nitrogen content contributes to an increase in the MR ratio and a reduction in the RA, in comparison with a case of a tunnel barrier containing no nitrogen.

Example 10

The production method is similar to that in the Example 8, but only the material for forming the tunnel barrier layer is different from that of Example 8 Particularly, the nitridation and oxidation process performed after first Al film formation and second Al film formation is different. A 0.6 nm thick film of Zn_(0.9)In₂ is formed by sputtering with a target having an alloy composition of Zn_(0.9)In₂. Thereafter, the above-described sample was moved to an oxidation chamber of which the inside was kept in an ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidation by introducing Ar, oxygen, and nitrogen in a state in which the substrate was heated at 250° C. First, plasma nitridation was performed for 1 minute at a partial pressure ratio of 1:15 to 25 (Ar:nitrogen) and a total gas pressure of 0.5 Pa. Then, after waiting until the pressure inside the oxidation chamber was equal to or less than an ultrahigh vacuum of 1×10⁻⁸ Pa or less, natural oxidation was performed for 5 to 300 seconds at a partial pressure ratio of 1:20:5 (Ar:oxygen:nitrogen) and a total gas pressure of 0.05 Pa. Then, the sample was returned to a film-forming chamber, and a film of Zn_(0.9)In₂ with a thickness of 0.5 nm was formed. The above-described sample was moved to the oxidation chamber of which the inside was kept in an ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidation and inductively coupled plasma oxidation by introducing Ar and oxygen. The natural oxidation time was 30 seconds, and the inductively coupled plasma oxidation time was 5 seconds. The partial pressure ratio of Ar to oxygen was 1:2 to 20, and the total gas pressure was 0.05 Pa.

A cubic structure in which the spinel structure was disordered was confirmed from an electron beam diffraction image. The composition of the tunnel barrier layer having a thickness of 1.1 μm was analyzed using an oxygen and nitrogen analyzer, and as a result, as a standard of the composition ratio, the sum of the oxygen content and the nitrogen content was defined as 1, and relative amounts of oxygen and fluorine were compared to each other. The lattice constant of the tunnel barrier layer was obtained using X-ray diffraction measurement.

FIG. 17 shows results of the X-ray diffraction measurement for obtaining the lattice constant regarding the oxidized and nitrided element. The lattice constant linearly changes at a nitrogen content of up to approximately 8%, and can be thought to change as an effect of the introduction of the nitrogen to the crystal lattice. In addition, the fact that the lattice constant changes even in a case where the nitrogen content is 11% indicates that the tunnel barrier layer of Example 9 may contain at least 11% of nitrogen.

FIG. 18 shows results of the measurement of the magnetoresistance effect of the oxidized and nitrided element at a bias voltage of 80 mV. The horizontal axis represents the nitrogen amount in anions obtained by an oxygen and nitrogen analyzer, and the vertical axis represents the MR ratio. A peak shape is shown in which the MR ratio is increased at any nitrogen content in comparison with a case where the nitrogen content is zero, and the maximum MR ratio peak appears at a nitrogen content of 4%. In a case where the nitrogen content is 6.1% or greater, the MR ratio is reduced more than in a case where no nitrogen is contained. Accordingly, it is found that the nitrogen content is preferably 6% or less in the tunnel barrier layer of this example.

FIG. 19 shows results of the measurement of RA of the oxidized and nitrided element at a bias voltage of 80 mV. It is found that in a case where nitrogen is introduced to the tunnel barrier layer, the RA is reduced with an increase in the nitrogen amount. This indicates that the level of the nitrogen or fluorine partially substituted with oxygen functions, and a bandgap narrowing effect is made. In addition, from the fact that the minimum value of the RA is not observed with respect to the nitrogen content, it is found that a bandgap narrowing effect is made in proportion to the amount of the introduced nitrogen. In this example, the nitrogen content contributes to a reduction in the RA in any case.

From the above evaluation, it is found that at least the nitrogen is contained in an amount of up to 11% of the anion content in the tunnel barrier layer, and in a region where the nitrogen content is 6% or less of the anion content, any nitrogen content contributes to an increase in the MR ratio and a reduction in the RA, in comparison with a case of a tunnel barrier containing no nitrogen. In addition, in a region where the nitrogen content is greater than 6% and not greater than 11%, the MR ratio is reduced more than in a case of a material in which nitrogen is introduced to the tunnel barrier layer, but the RA is continuously reduced. For example, in magnetic sensors, magnetic heads, MRAMs, high-frequency application products, and the like requiring a reduction in the resistance of an element, even in a case where the MR ratio is reduced, total device characteristics are improved with a reduction in the RA, and thus 6% or greater of the nitrogen content is also effective.

Example 11

The production method is similar to that in the Example 1, but only the material for forming the tunnel barrier layer is different from that of Example 1. A 0.6 nm thick film of Mg_(0.9)Al₂ is formed by sputtering with a target having an alloy composition of Mg_(0.9)Al₂. Thereafter, the above-described sample was moved to an oxidation chamber of which the inside was kept in an ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural fluorination by introducing Ar, oxygen, and fluorine in a state in which the substrate was heated at 250° C. First, natural fluorination was performed for 1 minute at a partial pressure ratio of 1:10 to 50 (fluorine:Ar) and a total gas pressure of 0.01 Pa. Then, after waiting until the pressure inside the oxidation chamber was equal to or less than an ultrahigh vacuum of 1×10⁻⁸ Pa or less, natural oxidation was performed for 20 seconds at a partial pressure ratio of 1:25:0.1 (Ar:oxygen:fluorine) and a total gas pressure of 0.05 Pa. Then, the sample was returned to a film-forming chamber, and a film of Mg_(0.9)Al₂ with a thickness of 0.5 nm was formed. The above-described sample was moved to the oxidation chamber of which the inside was kept in an ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidation and inductively coupled plasma oxidation by introducing Ar and oxygen. The natural oxidation time was 30 seconds, and the inductively coupled plasma oxidation time was 5 seconds. The partial pressure ratio of Ar to oxygen was 1 to 20, and the total gas pressure was 0.08 Pa.

A cubic structure in which the spinel structure was disordered was confirmed from an electron beam diffraction image. The composition of the tunnel barrier layer having a thickness of 1.1 μm was analyzed using an oxygen and nitrogen analyzer, and as a result, as a standard of the composition ratio, the sum of the oxygen content and the fluorine content was defined as 1, and relative amounts of oxygen and fluorine were compared to each other. The lattice constant of the tunnel barrier layer was obtained using X-ray diffraction measurement.

FIG. 20 shows results of the X-ray diffraction measurement for obtaining the lattice constant regarding the oxidized and fluorinated element. The lattice constant linearly changes at a nitrogen content of up to approximately 3%, and can be thought to change as an effect of the introduction of the nitrogen to the crystal lattice. In addition, the fact that the lattice constant changes even in a case where the fluorine content is 5.2% indicates that the tunnel barrier layer of this example may contain at least 5.2% of fluorine.

FIG. 21 shows results of the measurement of the magnetoresistance effect of the oxidized and fluorinated element at a bias voltage of 80 mV. The horizontal axis represents the nitrogen amount in anions obtained by an oxygen and nitrogen analyzer, and the vertical axis represents the MR ratio. In comparison with a case where the fluorine content is zero, the MR ratio is increased at any nitrogen content, an increase in the MR ratio relative to the fluorine content is reduced at a fluorine content of 1.4% or greater, and the maximum MR ratio is obtained at a fluorine content of 3.5%. Accordingly, the nitrogen content is preferably 3.5% or less in the tunnel barrier layer of this example.

FIG. 22 shows results of the measurement of RA of the oxidized and fluorinated element at a bias voltage of 80 mV. It is found that in a case where fluorine is introduced to the tunnel barrier layer, the RA is reduced with an increase in the fluorine amount. This indicates that the level of the nitrogen or fluorine partially substituted with oxygen functions, and a bandgap narrowing effect is made. In addition, there is a tendency that the value of the RA is minimum at a fluorine content of 2.2%, and the RA is increased again at a fluorine content exceeding 2.2%. This indicates that the fluorine introduced excessively functions as a scatterer of conduction. It is found that fluorine is preferably contained for reducing the RA of the tunnel barrier layer. In addition, it is found that the fluorine content is more preferably at least 1.4% to 3.5% from the peak shape of FIG. 22.

From the above evaluation, it is found that at least the fluorine is contained in an amount of up to 11% of the anion content in the tunnel barrier layer, and in a region where the nitrogen content is 5.2% or less of the anion content, any fluorine content contributes to an increase in the MR ratio and a reduction in the RA, in comparison with a case of a tunnel barrier containing no fluorine. In addition, in a region where the fluorine content is greater than 3.5%, the RA is continuously reduced more than in a case of a material in which no fluorine is introduced to the tunnel barrier layer. For example, in magnetic sensors, magnetic heads, MRAMs, high-frequency application products, and the like requiring a reduction in the resistance of an element, even in a case where the MR ratio is reduced, total device characteristics are improved with a reduction in the RA, and thus 3.5% or greater of the fluorine content is also effective.

Example 12

The production method is similar to that in the Example 1, but only the material for forming the tunnel barrier layer is different from that of Example 1 Å 0.6 nm thick film of Mg_(0.9)Al₂ is formed by sputtering with a target having an alloy composition of Mg_(0.9)Al₂. Thereafter, the above-described sample was moved to an oxidation chamber of which the inside was kept in an ultrahigh vacuum of 1×10⁻⁸ Pa or less, and the substrate was cooled to −70 to −30 degrees. Then, plasma nitridation was performed for 1 minute at a partial pressure ratio of 1:25 (Ar:nitrogen) and a total gas pressure of 1 Pa. Then, after waiting until the inside of the oxidation chamber was under an ultrahigh vacuum of 1×10⁻⁸ Pa or less, the substrate was heated at 250° C., and natural oxidation was performed for 20 seconds at a partial pressure ratio of 1:25:5 (Ar:oxygen:nitrogen) and a total gas pressure of 0.05 Pa. Then, the sample was returned to a film-forming chamber, and a film of Mg_(0.9)Al₂ with a thickness of 0.5 nm was formed. The above-described sample was moved to the oxidation chamber of which the pressure inside the oxidation chamber was equal to or less than an ultrahigh vacuum of 1×10⁻⁸ Pa or less, and the substrate was cooled to −70 to −30 degrees. Then, natural oxidation and inductively coupled plasma oxidation were performed by introducing Ar and oxygen. The natural oxidation time was 30 seconds, and the inductively coupled plasma oxidation time was 5 seconds. The partial pressure ratio of Ar to oxygen was 1 to 20, and the total gas pressure was 0.08 Pa.

(Cross-Section Analysis of Example 12)

A volume ratio of the lattice-matched part (lattice-matched portion) with respect to the volume of the entire tunnel barrier layer was calculated as described above using a cross-section transmission electron microscope (TEM) image and an image obtained by removing electron beam diffraction spots in a direction other than a stacking direction in an electron beam diffraction image obtained by Fourier-transforming the TEM image and by then performing inverse Fourier transformation.

FIG. 24 is a structural schematic diagram of a cross-section including a direction parallel to the stacking direction of Example 12. From the high-resolution cross-section TEM image obtained in Example 12, it was found that a size (width) of the film surface of the lattice-matched part of the tunnel barrier layer in a direction parallel thereto was 30 nm or less in any part. 30 nm is about 10 times the lattice constant of the CoFe alloy that is the material of the first ferromagnetic metal layer and the second ferromagnetic metal layer, and mutual interference of the spin-polarized electrons in a direction perpendicular to the tunneling direction before or after coherent tunneling can be thought to be intensified about 10 times the lattice constant.

FIG. 25 is a diagram showing a volume ratio of the lattice-matched part (lattice-matched portion) with respect to the volume of the entire tunnel barrier layer of Example 12 and characteristics of the element. FIG. 23(A) is a diagram showing element resistance (Rp) when magnetization directions of the first ferromagnetic metal layer and the second ferromagnetic metal layer are parallel to each other. FIG. 25(B) is a diagram showing element resistance (Rap) when magnetization directions of the first ferromagnetic metal layer and the second ferromagnetic metal layer are antiparallel to each other. FIG. 25(C) is a diagram showing a magnetoresistance ratio of the element. The Rp tends to be reduced when the proportion of the lattice-matched part in which the tunnel barrier layer is lattice-matched to both of the first ferromagnetic metal layer and the second ferromagnetic metal layer is in the range of 65% to 95%. Regarding this, in a case where the tunnel barrier layer is completely lattice-matched, spin-polarized electrons interfere with each other during passing through the tunnel barrier layer, and thus it is thought that the electrons do not easily pass through the tunnel barrier layer. In contrast, in a case where the lattice-matched parts, in which lattices are matched, partially exists, the interference of spin-polarized electrons during passing through the tunnel barrier layer is appropriately cut in a part in which lattices are not matched, and thus the spin-polarized electrons easily pass through the tunnel barrier layer. As a result, it is thought that a tendency of a reduction in the Rp is observed. At the same time, a tendency of a slight increase in the Rap is observed when the proportion of the lattice-matched portion is in the range of 65% to 95%. This indicates that even when the magnetization directions of the first ferromagnetic metal layer and the second ferromagnetic metal layer are antiparallel to each other, the interference between domains is eased, and it is found that the spin-polarized electrons passing through the tunnel barrier layer are magnetically scattered.

Comparative Example 1

The production method is similar to that in the Example 1, but only the material for forming the tunnel barrier layer is different from that of Example 1. A 0.6 nm thick film of MgAl₂ is formed by sputtering with a target having an alloy composition of MgAl₂. Thereafter, the above-described sample was moved to an oxidation chamber of which the inside was kept in an ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidation by introducing Ar and oxygen. The natural oxidation time was 10 seconds, the partial pressure ratio of Ar to oxygen was 1 to 25, and the total gas pressure was 0.05 Pa. Then, the sample was returned to a film-forming chamber, and a film of MgAl₂ with a thickness of 0.5 nm was formed. The above-described sample was moved to the oxidation chamber of which the inside was kept in an ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidation and inductively coupled plasma oxidation by introducing Ar and oxygen. The natural oxidation time was 30 seconds, and the inductively coupled plasma oxidation time was 5 seconds. The partial pressure ratio of Ar to oxygen was 1 to 20, and the total gas pressure was 0.08 Pa.

(Characteristics of Comparative Example 1)

As a result of the measurement of the magnetoresistance effect, it was found that the MR ratio at a bias voltage of 80 mV was 96%, and the area resistance (RA) of the element was 2 Ω·μm². In addition, it was confirmed that the tunnel barrier layer had a spinel structure based on an electron beam diffraction image.

Comparative Example 2

The production method is similar to that in the Example 1, but only the material for forming the tunnel barrier layer is different from that of Example 1 Å 0.6 nm thick film of Mg_(0.9)Al₂ is formed by sputtering with a target having an alloy composition of Mg_(0.9)Al₂. Thereafter, the above-described sample was moved to an oxidation chamber of which the inside was kept in an ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidation by introducing Ar and oxygen. The natural oxidation time was 10 seconds, the partial pressure ratio of Ar to oxygen was 1 to 25, and the total gas pressure was 0.05 Pa. Then, the sample was returned to a film-forming chamber, and a film of Mg_(0.9)Al₂ with a thickness of 0.5 nm was formed. The above-described sample was moved to the oxidation chamber of which the inside was kept in an ultrahigh vacuum of 1×10⁻⁸ Pa or less to perform natural oxidation and inductively coupled plasma oxidation by introducing Ar and oxygen. The natural oxidation time was 30 seconds, and the inductively coupled plasma oxidation time was 5 seconds. The partial pressure ratio of Ar to oxygen was 1 to 20, and the total gas pressure was 0.08 Pa.

(Characteristics of Comparative Example 2)

As a result of the measurement of the magnetoresistance effect, it was found that the MR ratio at a bias voltage of 80 mV was 123%, and the area resistance (RA) of the element was 1.2 Ω·μm². In addition, it was confirmed that the spinel structure is a disordered cubic structure based on an electron beam diffraction image.

(Comparison of Examples with Comparative Examples)

Table 1 shows the examples and the comparative examples.

TABLE 1 RA [Ω · μm²] MR Ratio [%] Examples Example 1 0.5 166 Example 2 0.5 148 Example 3 0.44 142 Example 4 0.39 125 Example 5 0.15 86 Example 6 0.41 177 Example 7 0.45 152 Comparative Examples Comparative 2 96 Example 1 Comparative 1.2 123 Example 2

Comparison of Examples and Comparative Examples shows that both MR ratio and RA are better for Examples. Particularly, it is found that by substituting oxygen ions partially with nitrogen ions or fluorine ions, the RA is significantly reduced, and a large substitution effect is obtained.

(Comparison of Examples 8 to 11)

The results of Examples 8 to 11 are summarized in Tables 2 and 3.

TABLE 2 Maximum Range of Lattice Content Optimum Content Constant at Optimum (nitrogen/ Estimated from Lattice Content fluorine) Constant [Å] Example 8 8% 3.5% or less   8.0879 to 8.0921 Example 9 8% 2% or less 7.9186 to 7.92  Example 10 11%  6% or less 8.9286 to 8.9335 Example 11 5.2%  3.5% 8.0479 to 8.0459

TABLE 3 Region Having MR Ratio Region where Region Having Region Where Improvement MR Ratio is RA Improvement Ra is Effect Optimum Effect Optimum Example 8 8% or less 0.5% to 3.5% 8% or less 0.5% to 3.5% Example 9 8% or less 0.5% to 3.5% 8% or less 0.3% to 2%   Example 10 6% or less 6% or less 11% or less  11% or less Example 11 5.2% 3.5% or less   5.2% or less  1.4% to 3.5%

Based on Tables 2 and 3, it is effective that the nitrogen or fluorine concentration is at least 5.2% or less in any case to exhibit an improvement in the MR ratio or the RA.

In a case where the lattice constant of the tunnel barrier layer is 7.9186 to 8.9335 Å, it was observed that nitrogen or fluorine was contained in the tunnel barrier layer. At least the MR ratio was the same or higher, and the resistance was reduced.

In addition, there is an optimum range of nitrogen or fluorine content in each combination of the constituent elements for an optimum MR ratio or RA, and the optimum range is a content of 0.5% to 2%.

INDUSTRIAL APPLICABILITY

It is possible to provide a magnetoresistance effect element that obtains a high MR ratio with lower RA than a TMR element using a conventional spinel tunnel barrier.

EXPLANATION OF REFERENCE

-   -   100: MAGNETORESISTANCE EFFECT ELEMENT     -   1: SUBSTRATE     -   2: UNDERLAYER     -   3: TUNNEL BARRIER LAYER     -   4: CAP LAYER     -   5: ELECTRODE LAYER     -   6: FIRST FERROMAGNETIC METAL LAYER     -   7: SECOND FERROMAGNETIC METAL LAYER     -   8: ELECTRODE PAD     -   71: CURRENT SOURCE     -   72: VOLTMETER 

What is claimed is:
 1. A method of manufacturing a ferromagnetic tunnel junction comprising: a step of forming a first ferromagnetic metal layer on a substrate; a step of forming a tunnel barrier layer on the first ferromagnetic layer; and a step of forming a second ferromagnetic metal layer on the tunnel barrier layer, wherein the step of forming a tunnel barrier layer comprises a plurality of steps of forming a metal layer represented by a composition formula Mg_(1-x)Al_(x) (0<x<1) and a step of oxidizing the metal layer formed in at least one of the plurality of steps of forming a metal layer.
 2. The method of manufacturing a ferromagnetic tunnel junction according to claim 1 further comprising: a step of natural oxidizing the substrate by introducing at least Ar, oxygen, and nitrogen in a state in which the substrate is heated.
 3. The method of manufacturing a ferromagnetic tunnel junction according to claim 1 further comprising: a step of inductively coupled plasma oxidizing the substrate by introducing at least Ar, oxygen, and nitrogen in a state in which the substrate is heated.
 4. The method of manufacturing a ferromagnetic tunnel junction according to claim 1 further comprising: a step of natural oxidizing the substrate by introducing at least Ar, fluorine, and oxygen in a state in which the substrate is heated.
 5. The method of manufacturing a ferromagnetic tunnel junction according to claim 1 further comprising: a step of inductively coupled plasma oxidizing the substrate by introducing at least Ar, fluorine, and oxygen in a state in which the substrate is heated.
 6. The method of manufacturing a ferromagnetic tunnel junction according to claim 1 further comprising: a step of natural oxidizing the substrate by introducing at least Ar, oxygen, and nitrogen after the substrate temperature is lowered.
 7. The method of manufacturing a ferromagnetic tunnel junction according to claim 1 further comprising: a step of natural oxidizing the substrate by introducing at least Ar, fluorine, and oxygen after the substrate temperature is lowered.
 8. The method of manufacturing a ferromagnetic tunnel junction according to claim 1, the substrate temperature is lowered to −70 to −30 degrees.
 9. The method of manufacturing a ferromagnetic tunnel junction according to claim 2 further comprising: a step of inductively coupled plasma oxidizing the substrate by introducing at least Ar, oxygen, and nitrogen in a state in which the substrate is heated.
 10. The method of manufacturing a ferromagnetic tunnel junction according to claim 2 further comprising: a step of inductively coupled plasma oxidizing the substrate by introducing at least Ar, fluorine, and oxygen in a state in which the substrate is heated.
 11. The method of manufacturing a ferromagnetic tunnel junction according to claim 6, the substrate temperature is lowered to −70 to −30 degrees.
 12. The method of manufacturing a ferromagnetic tunnel junction according to claim 7, the substrate temperature is lowered to −70 to −30 degrees. 